hal: fix resource leak issues in platform.c

- fix resource leak issues related to mixer
  controls and file handles

Change-Id: I3675da4504a93a084ad582e5e6eb7c75f38e736e
diff --git a/hal/msm8960/platform.c b/hal/msm8960/platform.c
index e7d6920..be50289 100644
--- a/hal/msm8960/platform.c
+++ b/hal/msm8960/platform.c
@@ -243,6 +243,7 @@
     adev->audio_route = audio_route_init(MIXER_CARD, MIXER_XML_PATH);
     if (!adev->audio_route) {
         ALOGE("%s: Failed to init audio route controls, aborting.", __func__);
+        mixer_close(adev->mixer);
         return NULL;
     }